/Engine/Source/Runtime/Slate/Public/Framework/MultiBox/MultiBoxBuilder.h
Adds a sub-menu which is a menu within a menu
void AddWrapperSubMenu ( const [FText](API\Runtime\Core\Internationalization\FText) & InMenuLabel, const [FText](API\Runtime\Core\Internationalization\FText) & InToolTip, const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > & InSubMenu, const [FSlateIcon](API\Runtime\SlateCore\Textures\FSlateIcon) & InIcon )